1. Field of the Invention
The present invention relates to coke oven regenerators, that area of a battery of coke ovens in which the waste gases produced by combustion are used to preheat the fuel gas mixture and/or air before it is fed into the combustion chambers, and the construction of those regenerators.
2. Description of the Prior Art
In the known coke oven regenerators, bricks, manufactured from a refractory material, are used to alternately absorb and radiate heat. The hot waste gases in the combustion chambers of a coke oven are channelled into the regenerator and over, through, and around the checker brick contained therein. These hot waste gases heat up the checker bricks. At a given point in time the flow of hot gases is rechannelled into the companion regenerator, which has been on the cooling portion of its cycle. In coke oven batteries heated with a fuel gas mixture of low calorific value, the fuel gas mixture, which is burned in the coke oven to provide heat for the coking process, is made up of air and low Btu lean gas. At a given time, the low Btu lean gas is channelled through one quarter of the overall regenerator or one half of the waste gas preheated regenerator. Air is channelled through the balance of the preheated regenerator. Hot waste gases, at this point, are conducted through the other half of the overall regenerator which has been previously cooled by earlier passage of low Btu gas and air. The low Btu lean gas and air are channelled across the preheated bricks, thus preheating these components of the fuel gas mixture, resulting in a higher combustion temperature per given volume of that fuel gas mixture. In coke oven batteries heated with a fuel gas mixture of higher calorific value, using a rich gas of high Btu content, the combustion air used to burn the fuel is not channelled across the preheated checker bricks, but that air is preheated to a lesser degree outside of the regenerator. The higher temperature per given volume of fuel gas mixture allows less fuel to be used to maintain a temperature within the coke oven sufficient to produce coking of coal, thus enhancing economy of operation. The efficiency of a coke oven regenerator depends on the ability of the checker brick to transfer heat while at the same time minimizing the degree of restriction of flow of the various gases, including waste gas, air or fuel gas, which move through the regenerator.
The object of developing efficiency in coke oven regenerator checker brick is threefold. Firstly, with a more efficient brick, fewer brick can be used to achieve an equivalent result. This allows a reduction in size, in particular the height, of coke ovens, resulting in less of an initial capital investment in construction. Secondly, a reduction in the quantity of fuel gas used can be achieved, releasing a valuable energy producer for other uses. Thirdly, higher heat can be achieved in the coke oven by increasing the efficiency of the checker brick. The result is a faster coking cycle which, in turn, can increase daily production of coke.
Many intricate designs of refractory regenerator brick have been developed to increase the surface area of the bricks thus enhancing the transfer of a greater quantity of heat per given unit of time. Specifically, this is achieved by inserting slots into the bricks, then corrugating the surfaces of those slots, and finally developing cross-channels in the bricks, all of which serve to increase the area of the brick which is exposed to the gases. However, none of these has been developed to the point of commercial success for use in coke oven regenerators.
One limitation on this line of development is found in the fact that for the checker brick to do its job, it must retain a certain minimum mass of refractory material. This is necessary to retain sufficient heat from the waste gases to preheat the fuel gas and/or air after the gases are rechannelled. Another limitation is found in the fact that any reduction in the total open cross-sectional area of the apertures of the checker brick, with respect to the total cross-sectional area of the regenerator, restricts the flow of gases through the regenerator and increases the pressure losses of the system. A third limitation is found in the minimal size of corrugation spacing that is operable over an extended period of time. Coke oven waste gases, and blast furnace gas when used, contain particulate matter which will clog up the corrugations over a period of time if those corrugations are too small and/or placed too closely together.
Finally, a fourth limitation is found in the cost of the brick itself. The more intricate the design of the apertures and the thinner the cross section of the walls, the more expensive it is to manufacture the checker brick. Two basic methods are available to manufacture refractory checker brick. The first is by casting, where the refractory material is poured into a mold in which it must be left for an extended period of time to set up. The green brick is then ejected from the mold and placed in heated means for drying to drive out the moisture. The dried brick is then placed in a high temperature kiln where it is cured by firing. This cures the brick into a finished product. The second process, much more economical where it can be used, consists of a die through which viscous refractory material is pushed by a press to form a slug. The slug is then re-pressed into a mold and ejected in the form desired. This refractory form is then dried and placed directly into a kiln to be cured. This second process is called the re-press method. However, this re-press process suffers from a deficiency. Refractory forms, with minimal and intricate cross-sectional areas and designs, such as those illustrated in British Patent No. 121,536 and in German Auslegeschrist No. 2,425,931, readily crack and crumble during the curing phase, as the temperature is raised from ambient to that of formation of green brick. Thus it is practically impossible to manufacture such shapes by the re-press method. This problem does not occur in manufacturing such shapes as cast brick. But cast bricks cost more to make due to the extra set-up time and manufacturing steps involved.
There is a need for a coke oven regenerator checker brick which provides sufficient surface area for high efficiency heat transfer while at the same time providing enough mass for heat retention, sufficiently large apertures and face configuration to prevent clogging from particulate matter, and which can be manufactured by the extrusion and re-press process.